Radiation therapy uses high-energy rays or particles to kill cancer cells. It may be used after surgery to destroy any cancer cells that remain in the breast, chest wall, or underarm area.

If a patient needs chemotherapy after surgery, he also may receive radiation treatment once chemotherapy is completed. The oncologist, breast surgeon, and radiation oncologist will work together to decide the best sequence of treatments.

How the radiation therapy is given depends on the stage of the cancer being treated and the results of the pathology tests after breast surgery.

The usual course of radiation therapy includes daily treatments five days a week for five to seven weeks. By giving smaller amounts of radiation each day, rather than giving all the radiation at once, the radiation oncologist ensures that the majority of healthy cells have the time they need to repair radiation-induced damage in between treatments, while cancer cells become inactive.

Each radiation session generally lasts less than an hour. Radiation is routinely given after breast-conserving surgery and is sometimes used after mastectomy depending on the number of lymph nodes with cancer, the size of the cancer, and how far away the cancer is from the margin or edge of the breast tissue that was removed.